public class FixedSizeStack{
	private Stack stack;
	public FixedSizeStack(Stack stack){
	this.stack = stack;
}

public void Push(object item){
	if(stack.Count() == 10){
		throw new Exception("full");
	}
	stack.Push(item);
	}
//...
}

public void TestPush(FixedSizeStack stack, object item){
	stack.Push(item);
}